I did some quick research on it. It was literally the first English "tractor" before they called them tractors. It's one of eight and won a silver in 1903 and gold in 1904. The inventor died in 1907.
Although they had steam tractors at the time ( called " traction engines" ), they took a great amount of time to get them ready to do actual work. These fancy gas engines just required checking fluid levels and getting them started. Another big plus was safer operation compared to high pressure steam.
Part of the price is history, part extremely low numbers of units made and more than one person with very deep pockets. A BIG plus it's an actual working example